In 2004 an important discovery was published by Geim and Novoselov regarding the exceptional electronic properties of graphene in a suspended form. Subsequently, many researchers have studied graphene material properties and determined graphene has other interacting thermal, chemical, optical and mechanical properties. However, very little research has been done on exploring tribological properties of graphene or graphene oxide. Graphene or graphene oxide are considered as good candidates as self-lubricating materials, due to their chemically inert nature, strong mechanical properties and low shear strength on its densely packed and atomically smooth surfaces. Since it is ultrathin, even with multi-layers, it can be transferred onto MEMS/NEMS devices for operation and use at the oscillating, rotating and sliding contacts to reduce stiction, friction and wear.
The term superlubricity is defined as a regime of motion in which friction vanishes or almost vanishes. However, it is never zero; therefore, it should not be confused with other similar terms such as superconductivity or superfluidity. Superlubricity may occur when two crystalline surfaces slide over each other in dry incommensurate contact. This effect, also called structural lubricity, was suggested in 1991 and verified with great accuracy between two single crystal graphite surfaces in 2004. Similar effect of ultra-low friction has also been observed between the interwalls of two nested multiwalled carbon nanotubes. Atoms in graphite are oriented in a hexagonal manner and form an atomic hill-and-valley landscape, which looks like an egg-crate. When the two graphite surfaces are in registry (every 60 degrees), the friction force is high. When the two surfaces are rotated out of registry, the friction is greatly reduced. This is like two egg-crates which can slide over each other more easily when they are “twisted” with respect to each other. Since this effect is due to the incommensurability of lattice planes sliding against each other, the effect is restricted to material interactions at the nanoscale. At macro-scale, this effect diminishes due to the loss of structural order and presence of many defects. It is therefore understood why superlubricity is very difficult to achieve at macro-scale levels.